1. Field of the Invention
The present invention relates to a method and device for continuously locating vehicles. A computer is connected to a path data measuring unit that emits a measured value w corresponding to a distance covered. The computer is further connected to a path data memory, in which the route to be traveled, the position of bus stops, and the distances between stops are stored.
In order to guarantee a smooth functioning of medium-sized and large traffic operations, in particular in local public transportation (OPNV), modem computer-controlled operational control systems (RBL) are used, as described in "Modem Operational Control Systems on the Basis of Data Radio Networks," by Dr. J. Gehrig in "Verkehr und Technik," special edition, Issue 12, Erich Schmidt Verlag, Berlin, 1992. The communication between the system units of a modem operational control system shown in FIG. 1: the control headquarters (LST), the vehicles LB as well as local control devices, for example for influencing traffic signals LSA, which control the flow of traffic, normally takes place via radio in real time. The transfer of data from point to point, for example from stationary points along the route to the vehicles LB, often takes place via an infra-red connection. To control the peripheral system units LB, LSA, XP, XT and for the cyclical collection of the immediate operating data, digital telegrams are used, which are transformed into analogue signals (modulation)and broadcast over at least one data channel. To optimize the functions within the control system, relevant local specific information is called up and analyzed, preferably by the control headquarters LST. Knowledge of the exact position of each vehicle LB is of importance not only for the control headquarters LST, but also for the computer systems placed in the vehicles LB. A locating system which delivers precise data concerning the location of the vehicle LB is the prerequisite for a specific local delivery of information about passengers, the control of traffic signals LSA, as well as the calculation of schedule deviations. For instance, if two public buses (for example LB30 and LB299) are approaching an intersection, a computer positioned at that intersection, which determines which bus LB would reach the intersection first, could control the traffic signal LSA in such a way that both buses LB30 and LB299 can cross the intersection with as little delay as possible. Further, the vehicle position could be used as an input quantity for controlling the ticket machines in the individual vehicles LB.
By means of satellites or beacons, the position of a vehicle LB can be ascertained in a known fashion with minimal error deviations. These locating systems are, however, expensive and do not always satisfy the requirements placed on them. For example, the radio connection between moving vehicles LB to the satellite can occasionally be interrupted. Beacons, which would have to be present in large numbers, can only deliver exact position data at certain points.
Further, a device is known by which measured path data are corrected by means of data corresponding to a street map in a manner described in the following. The determination of the distance traveled takes place by means of an on-board computer, preferably by measuring the revolutions of a wheel with a known diameter. Over longer distances, greater deviations between the distance measured and the distance actually traveled can arise due to indications of slippage, changes in wheel diameter, or through veering or passing maneuvers. Therefore, the measured distance must be corrected regularly. For this purpose, as shown in FIGS. 2 and 3, each bus stop H is, in the data memory, assigned a target stopping position s as well as a maximal capture range f. Each maximal capture range f is chosen such that due to it, the measured value w of the path route traveled, with consideration of the possible occurrence of measuring error e, is always taken when the vehicle LB stops at the relevant bus stop H. If the vehicle LB stops within the capture range f, this is registered by the on-board computer as a stop at a defined bus stop H. The measured value w, which can be taken, for example, from the front of the vehicle LB can thus be compared with the position data in memory storage of the corresponding target stopping positions s. In order that the error deviation of the measured value w do not become too large, and even at the next bus stop H are still within the capture range f, when the vehicle LB is in the stopping range d, each stop at a bus stop H is used to make a correction to measured value w. This is based on the vehicle always stopping near the target stopping range s. It is thereby assumed that the deviation of measured value w from the target stopping position s has to do primarily with a faulty measurement, and that the actual position of the vehicle lies approximately in between measured value w and the target stop position s. Measured value w is thus corrected by half the difference between measured value w and the distance value of target stop positions.
This method, by which the maximum area of capture range f is determined statically, exhibits considerable disadvantages. Capture range f is exclusively dependent on the distance which was covered from the place where the measured value was most recently corrected. If a correction was, for instance, made by a beacon directly before a bus stop H, a very small capture range f results up until this stop H, which can easily be missed, if the vehicle LB does not stop near the target stopping position s. The vehicle computer IR will not recognize a stop at the bus stop H in this case, and it must therefore be entered manually by the driver. The automatic delivery of information relevant to a particular bus stop, for example regarding connections, does not take place. In addition, at bus stops (for example FIG. 2 and FIG. 4, stop H.sub.n+1) which have a greater length, serious errors arise when correcting the measured value w. In bus stop H.sub.n+1, shown in more detail in FIG. 4, a vehicle AM is parked in such a way that vehicle LB can not drive up to the target stopping position S.sub.n+1. The capture range f can thus be very easily missed, as described above. However, if the on-board computer IR in vehicle LB determines that the stop occurred within the capture range f, this will be registered as a stop at bus stop H.sub.n+1. Although the vehicle LB did not drive up to target stopping position s and measured value w gives the actual position of the vehicle LB precisely, the computer IR assumes that the vehicle LB did stop precisely at the target stopping point S.sub.n+1. The measured value w is thus corrected by half diff/2 of the difference diff between the measured value w and the distance value of the target stopping position S.sub.n+1. Since the measured value w was originally correct, an error is introduced, which corresponds to the value diff/2, through this intended correction at the bus stop H.sub.n+1. If the next bus stop H is not far away, and due to the short distance only a small capture range f results, this faulty correction of measured value w will lead with great probability to capture range f being missed. The measured value w, which was inexactly corrected by means of the known method, thus usually exhibits considerable deviations in regard to the actual position of the vehicle LB. Correspondingly, it is not possible to control, for example, the ticket machines exactly, so that a correct calculation of the travel costs cannot be guaranteed. The appearance of errors in measurement also make themselves disturbingly known in the control of traffic or by the delivery of information in connection with the position. For instance, traffic signals are changed too early or too late, or specific local information will not be delivered on time to the passengers in the vehicle LB. Bus stops H will often be detected only when the capture ranges f have taken on maximum values. Thus the number of faulty detections steadily increases wherein the vehicle LB stops within a capture range f, not, however, within the corresponding stopping range d of a bus stop H, by which the correction method mentioned above functions.
Disadvantages to the known method also ensue if the route network is altered even slightly. The maximum values of the capture ranges f of bus stops H must be examined and re-fitted at considerable expense.